[C38] Knot meter location

[Phil Gay]

A very strange thing happened a couple of years ago.  I have a Raymarine
ST60 knotmeter.  It stopped working and I pulled the transducer with the
boat in the water, installed the factory plug, cleaned the transducer, and
replaced it.  The meter worked if the speed was less than a knot, but didn't
work above that speed.  I pulled the transducer and cleaned it several times
trying to solve the problem.

 

In the spring I hauled the boat for a prop inspection and noticed that there
was a small muscle growing on a short strand of grass immediately in front
of the transducer.  The water flow caused the muscle to pivot aft where it
blocked the knotmeter paddle from turning.  I wonder what the chances of
that happening again are.

 

Phil Gay

C38 049 Que Linda

Everett WA

 

From: listserve-bounces at catalina38.org
[mailto:listserve-bounces at catalina38.org] On Behalf Of S Orton
Sent: Friday, January 14, 2011 3:06 PM
To: Cat 38
Subject: Re: [C38] Knot meter location

 

Chuck,  I have Raymarine (about 10 years old) and it still works fine.  It
comes with a screw in plug, with o-rings, which I use when ever tied up for
long periods.  The kit comes with a finger nail bottle of instrument
antifouling paint.  Following instructions, the paddle wheel remain free to
this day.
Cheers, Steve O 

  _____  

Date: Fri, 14 Jan 2011 11:34:09 -0500
From: charles at finn.ws
To: listserve at catalina38.org
Subject: Re: [C38] Knot meter location

I will be installing my third version of the knotmeter early this spring.
When I upgraded last time to Navman, I could not get the original (flush
mount) paddle wheel out.  It seemed to be almost welded in and I gave up
after heating and hydraulic force wouldn't budge it.  Plus, the Signet hole
was larger than the Navman.   I am currently installing Raymarine which of
course is a different hole size (larger).   My research at the time was
extensive, but came down to essentially two observations.  First was that
the paddlewheel should be located where there is as little laminar flow
disruption as possible.  Generally this is as far away from your bow
waterline as you can get, but not so far back as to be disrupted by the
pressure wave generated by the keel, which is rather small and angled due to
the raked design of our keel.  Second is the preferred location is on the
centerline of the boat, but varying a bit to either side does not make much
difference.  So, I think your boatyard probably made the right call
regarding location although I would have a real problem with them varying
from explicit instructions! 

I have to admit that I probably keep installing a knot meter more out of
sentiment and for emergency purposes than usefulness these days (I still
have a lead-line on board and actually do use it).  Frankly, it was quite
disappointing ten years back when I first got GPS to discover how variable
the readings are based upon boat speed, slime, etc.   My chart plotter is so
much more accurate regarding VMG, SOG, etc. that I seldom refer to the
knotmeter other than to get excited when we are flying because it invariably
reads faster than we are really going.  But for the moment, what's the harm
in believing you are doing 13 knots!  I do agree with Tom's point regarding
tides and this can be important at times, but I tune with my chartplotter.

Chuck Finn
Mighty Quinn #114 (1981, with the knot meter just aft of the water tank
right inside the access door on the vee berth)

On 1/13/2011 10:46 PM, Steve Smolinske wrote: 

Does anyone have any knowledge on the location of the knot meter on the
centerline?  Peregrine is in the yard having mushroom mounts removed and
replaced with flush mounts.  I instructed in writing to the yard along with
a photo to place the knot meter on centerline 33% of the distance from the
keel to the waterline entry point.  They have placed it 1' in front of the
keel and stated that is the perfect location and any further forward it will
be subject to disturbance from the bow wave.  (yes they went ahead without
contacting me first)   We are going to talk about it tomorrow morning and Im
hoping someone has some definitive information I can use. Grrrr  Thanks

 

Steve

#312 Peregrine

Seattle

  

 
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